Transducers



W. H. RYMES Jul 3, 1 956 TRANSDUCERS 2 Sheets-Sheet 1 Filed Aug. 28,1952 "Hill 'r ii/ i: ll DJ.

IIIIIIH a El l ji W. H. RYMES TRANSDUCERS July 3, 1956 2 Sheets-Sheet 2Filed Aug. 28, 1952 l9 7' TOIPIVE Y United States Y atent TRANSDUCERSWilliam H. Rymes, Randolph, Mass., assignor to Raytheon ManufacturingCompany, Newton, Mass, a corporation of Delaware Application August 28,1952, Serial No. 306,875

4 Claims. (Cl. 340-41) This invention relates to a compressional wavetransducer and, more particularly, relates to means for increasing theeffective driving surface of a transducer to achieve greater directivityof the energy radiated therefrom.

An object of this invention is to provide means for increasing theeffective driving surface of a compressional wave transducer.

Another object of this invention is to provide a compressional wavetransducer having improved directivity for a given size.

A further object of this invention is to provide means for varying thefocal length of the beam of a compressional wave transducer as afunction of the shape of a reflector mounted near one face of saidtransducer.

As is well known in the art, the intensity of compressional wave energyat different points equidistant from a transducer is dependent upon thedimensions of the driving surface compared with the wave length of saidenergy. The energy is largely confined within a diver ing beam Whoseaxis is perpendicular to the center of the driving surface. The angle ofspread of the beam is proportional to the ratio of the wave length ofsaid energy to the dimensions of the driving surface. The larger thisratio is made, that is, the larger the area of the driving surface for agiven frequency, the greater the directivity from the transducer.

Pursuant to this invention, the directivity of a transducer having afirst generating surface in contact with the medium through whichtransmission of energy is required and a second generating surfaceopposite said first surface is increased with the aid of one or morereflectors so positioned adjacent said second surface of the transducerthat the compressional wave energy radiated from said second surface andreflected from said reflector or reflectors is in phase with the energyradiated from said first surface.

By adjusting the angle of the reflector or reflectors and thus the angleof incidence of the energy reaching the reflector after emission fromsaid second surface, the beam of compressional wave energy may befocused at any desired depth in said surrounding medium.

In the drawings:

Fig. l is a central longitudinal section view of a first embodiment of atransducer assembly according to the invention;

Fig. 2 is a view in elevation of the transducer assembly of Fig. 1illustrating certain principles of operation and omitting the transducersupporting means for the sake of clarity;

Fig. 3 is a plan view, partly in section, of the transducer assembly ofFig. l, the section being taken through line 33 of Fig. 1;

Fig. 4 is a fragmentary detail view of the transducer used in theassembly of Figs. 1 to 3;

Fig. 5 is a sketch illustrating certain operating principles ofthetransducer assembly shown in Figs. 1 to 3;

Patented July 3, 1956 Fig. 6 is a view illustrating the effectivedriving surface obtained with a conventional transducer;

Fig. 7 is a view showing the effective driving surface obtained with thetransducer assembly shown in Figs. 1 to 3;

Fig. 8 is a second form of reflector which may be used in a transducerassembly according to the subject invention;

Fig. 9 is a view in elevation, partly in section, of a second embodimentof a transducer assembly according to the invention utilizing thereflector shown in Fig. 8;

Fig. 10 is a view illustrating the effective driving surface obtainedwith a conventional transducer having an area equal to the base of thepyramidal re-entrant portion of the reflector of Fig. 9; and

Fig. 11 is a view showing the effective driving surface of thetransducer assembly shown in Fig. 9.

Referring to Figs. 1 to 4, a transducer assembly, generally indicated byreference numeral 10, comprises a magnetostrictive transducer 11 moldedin a substance 12 having an acoustical impedance substantially equal tothat of the medium into which the transducer is to operate. For example,if the medium is sea water, the substance 12 may be a type of rubberwhose wave impedance is substantially equal to that of the aforesaidmedium.

Although substance 12 is shown as a solid mass, it is possible to usecastor oil or other liquids having a suitable acoustical impedance, inwhich case it is necessary to provide proper supporting means fortransducer 11.

The molded mass 12 is encased in a housing 13 which, although shown asrectangular in Fig. 3, may be any convenient shape, such as rectangular,circular or oval. Housing 13 may be made of any material havingsufficient rigidity and mechanical strength.

Transducer 11 is illustrated in detail in Fig. 4; the body portion 11comprises a plurality of laminations 14 having elongated slots 15through which winding 16 may be inserted. The terminals of winding 16are adapted to be connected to the usual receiving and transmittingmeans, as is well known in the art.

The transducer need not be limited to the exact details shown in Fig. 4,and other types of magnetostrictive transducers may be used. Moreover,crystal transducers may be used in lieu of magnetostrictive transducers,if desired.

Transducer 11 has two opposed radiating surfaces 20 and 21; surface 20is adapted to contact a medium through which the compressional waveenergy is to be propagated.

A multi-surface reflector 17, which is opaque to compressional waveenergy, is positioned in housing 13 adjacent surface 21 of transducer11. Reflector 17 may comprise a solid metallic plate, as shown in Figs.1-3, or may comprise a metallic backing plate to which a coating havinggood reflecting properties is cemented or otherwise attached. Thiscoating, for example, may consist of a combination of cork and neoprenehaving several air cells. Since air is a good reflector of compressionalwave energy, the reflecting power of reflector 17 may be enhanced.

Energy radiated from surface 21 impinges upon re flector 17 and isreflected therefrom. The path of the compressional waves radiated fromsurfaces 21 of trans ducer 11 is shown by the broken lines 23 of Fig. 2.An inspection of Fig. 2 indicates that not only the energy from surface20 but also that from surface 21 is available for propagation into thedesired transmission medium in contact with surface 20'.

The radiating surface 20 resulting from the transducer of Figs. 1 to 3when reflector 17 is omitted is shown in Fig. 6. The effective radiatingsurface 26, resulting when transducer 11 is provided with a reflector,is shown in Fig. 7. For a reflector whose sides are positioned at anangle of forty-five degrees with surfaces 20 and 21, as shown in Figs. 1to 3, the area of the driving surface is doubled when a reflector isused.

words, the time required for the compressional waves from the variouspoints on surface 21 of transducer 11 to travel to reflector 17 and bereflected back to surface 20 is dependent upon the degree of spacingbetween the reflector and the transducer. By moving the entire reflectorup and down, an optimum distance d is reached at which the reflectedcompressional waves emerge from surface 20' in time phase with thecompressional waves radiated directly from surface 20 of transducer 11.By adjustment of the angles 6 shown in Fig. 5, a focusing of the beammay be accomplished For example, if angles n at p and are equal toforty-five degrees, and if either of angles 6 or or both are made largerthan forty-five degrees, the compressional waves reflected from surfaces24- and 25 will be bent inward toward the center of the transducer. Atsome point in the transmitting medium, dependent upon angles 9 or 0 orboth and also dependent on the angles p and the beam will be focused.Since the wave length of the compressional waves is of the order of fourinches, the amount of change in angle 6 necessary to focus the beam at adistance, say 100 feet, will be only a fraction of a degree. For thisreason, therefore, the adjustment of angles 0 and 0' is somewhatcritical. It is preferable, therefore, to preset the angle 0 whichsurfaces 24 and 25 of reflector 17 make with either surfaces 20 and 21of transducer 11 to correspond to the focal length desired and buildthis angle into the transducer.

The shape of the beam pattern may also be varied by selection ofreflectors. A second possible compound reflector 17' for use withtransducer 11 is shown in Figs. 8 and 9. Reflector 17' comprises ametallic sheet in the form of a frustum of a pyramid having a pyramidalreentrant portion whose apex lies in the plane of the base 27 of saidfrustum. The angles formed by any two adjacent surfaces impinged by thecompressional waves from transducer 11 are made substantially equal toforty-five degrees. Reflector 17' is positioned adjacent to and spacedfrom surface 21 of transducer 11, as in the case of reflector 17 ofFigs. 1 to 3 and 5.

The distance between the base 27 of reflector. 17 and surface 21determines the phasing between the compressional waves emitted directlyfrom surface 20 of transducer 11 and the reflected compressional wavesarriving at surface 20.

As in the embodiment of Figs. 13 and 5, the beam focus may be adjustedby varying slightly the slope of one or more of the surfaces ofreflector 17 V V The active surface of transducer assembly of Fig. 9 inthe absence of reflector 17' is equal to the area of surface of thetransducer 11 and is shown in Fig. 10, while the active surface obtainedwhen reflector 17 is used with the same transducer is shown by Fig. 11.Because of the reflection of energy from the surfaces of the pyramidalreentrant portion, as well as from the surfaces of the frustum of thepyramid, in the reflector 17' of Figs. 8 and 9, the effective drivingsurface of the transducer assembly of Figs. 8 and 9 is of squareconfiguration, rather than rectangular, and furthermore, is oriented atan angle of forty-five degrees with respect to that obtained without theuse of the reflector 17'. For this reason, the effective driving surfaceshown in Fig. 11 is positioned at an angle of forty-five degreesrelative to that shown in Fig. 10. A comparison with Fig. 10 indicatesthat the surface area and hence the directivity of transducer 10 of Fig.9 is increased over that for a similar transducer without a reflector.

The reflectors herein shown and described are merely illustrative; otherreflectors may be used besides the two types shown and described toaccomplish an increase in the efiective driving surface of thetransducer.

This invention is not limited to the particular details of construction,materials and processes described, as many equivalents will suggestthemselves to those skilled in the art. It is accordingly desired thatthe appended claims be given a broad interpretation commensurate withthe scope of the invention within the art.

' What is claimed is:

1. A device for transmission of compressional wave energy through amedium comprising'a transducer having a pair of opposed vibratingsurfaces, said transducer being mounted within a body of material havinga wave impedance substantially equal to that of said medium and havingone of said surfaces in physical contact with said medium, amulti-surface reflector secured to said body and positioned adjacent theother of said opposed surfaces, said reflector being in the form of afrustum of a pyramid having a pyramidal reentrant portion whose apexlies in the plane of the base of said frustum, said reflector beingadapted to reflect incident energy from said other surface in phase withthe energy radiated from said one surface, thereby increasing theeffective driving surface of said device to obtain greater directivitytherefrom.

2. A device as recited in claim 1 wherein said surfaces of saidreflector are disposed at an angle of forty-five degrees with saidopposed transducer surfaces.

3. A device for transmission of compressional wave energy through amedium comprising atransducer having a pair of opposed vibratingsurfaces, said transducer being mounted within a body of material havinga wave im pedance substantially equal to that of said medium and havingone of said surfaces in physical contact with said medium, amulti-surface reflector secured to said body and positioned adjacent theother of said opposed surfaces, said reflector being in the form of afrustum of a pyramid having a pyramidal reentrant portion whose apexlies in the plane of the base of said frustum, said reflector beingadapted to reflect incident energy from said other surface in phase withthe energy radiated from said one surface, thereby increasing theeffective driving surface of said device to obtain greater directivitytherefrom, said portions of said reflectors forming said frustum beingdisposed at an angle with respect to said opposed vibrating surfacesdiffering from forty-five degrees by a slight amount so that said beamis focused.

4. A device for transmission of a beam of compressional wave energythrough a medium comprising a transducer having a pair of opposedvibrating surfaces, said transducer being maintained Within a body ofmaterial having a wave impedance substantially equal to that of saidmedium and having one of said surfaces in physical contact with saidmedium, a reflector secured to said body and positioned adjacent theother of said opposed surfaces, said reflector having a first, pair ofadjacent surfaces arranged at an angle of substantially forty-fivedegrees with said other opposed surface and a second pair of angularlyadjustable surfaces, said second pair of surfaces being inclined at anangle with respect to said vibrating surfaces differing slightly fromforty-five degrees such that the beam is focused at a point Whosedistance from said transducer is dependent upon the deviation of saidangle from forty-five degrees.

References Cited in the file of this patent UNITED STATES PATENTS2,005,741 Hayes June 25, 1935 2,398,117 Rost Apr. 9, 1946 2,491,982Kincart Dec. 20, 1949 V FOREIGN PATENTS 379,649 Italy Apr. 1, 1940

